Light emitting diode (LED) lighting systems are becoming more prevalent as replacements for existing lighting systems. LEDs are an example of solid state lighting (SSL) and have advantages over traditional lighting solutions such as incandescent and fluorescent lighting because they use less energy, are more durable, operate longer, can be combined in red-blue-green arrays that can be controlled to deliver virtually any color light, and generally contain no lead or mercury. In many applications, one or more LED dies (or chips) are mounted within an LED package or on an LED module, which may make up part of a lighting unit, lamp, “light bulb” or more simply a “bulb,” which includes one or more power supplies to power the LEDs. An LED bulb may be made with a form factor that allows it to replace a standard threaded incandescent bulb, or any of various types of fluorescent lamps. LEDs can also be used in place of florescent lights as backlights for displays.
Translucent or transparent rigid materials may be used with LED lighting to provide diffusion, color mixing, to otherwise direct the light, to serve as an enclosure to protect the LEDs and/or other electronic components, or to provide a support for wavelength conversion material sometimes used to achieve accurate color. Wavelength conversion materials may produce white light when struck by light of a specified color, or may produce an additional color of light that mixes with other colors of light to produce white light, or another specific desired color of light. As an example, phosphor particles can be used as a wavelength conversion material. Phosphor absorbs light at one wavelength and reemits light at a different wavelength. Typically, phosphor particles are randomly distributed within a matrix of encapsulant material. The term phosphor can refer to materials that are sometimes also referred to as fluorescent and/or phosphorescent.
To be used as part of an LED lamp or LED lighting system, phosphor is often applied to or included in a transparent or translucent carrier or substrate. Thus, materials such as acrylic, glass or polycarbonate are often used in LED lighting systems as optical elements, both with and without phosphors. In lighting systems where the LEDs emit ultraviolet (UV) light, consumable UV-stabilizing additives are used in acrylic or polycarbonate substrates so that the material maintains its clarity and strength over time despite the UV exposure. Even in LED systems that generate small amounts of actual UV light, near UV light that may be emitted can be almost as damaging to polymers as UV light. For example, GaN LEDs emit vanishingly small amounts of actual UV light, but large amounts of deep blue, near UV light that can have the same effects as UV light on acrylic or polycarbonate substrates.